14,420 research outputs found
Evidence for Gamma-ray Jets in the Milky Way
Although accretion onto supermassive black holes in other galaxies is seen to
produce powerful jets in X-ray and radio, no convincing detection has ever been
made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10
kpc tall gamma-ray bubbles in our Galaxy may be a sign of earlier jet activity
from the central black hole. In this paper, we identify a gamma-ray cocoon
feature in the southern bubble, a jet-like feature along the cocoon's axis of
symmetry, and another directly opposite the Galactic center in the north. Both
the cocoon and jet-like feature have a hard spectrum with spectral index ~ -2
from 1 to 100 GeV, with a cocoon luminosity of (5.5 +/- 0.45) x 10^35 erg/s and
luminosity of the jet-like feature of (1.8 +/- 0.35) x 10^35 erg/s at 1 to 100
GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.Comment: 14 pages, 11 figures, accepted by Ap
The Extended Wronskian Determinant Approach and the Iterative Solutions of One-Dimensional Dirac Equation
An approximation method, namely, the Extended Wronskian Determinant Approach,
is suggested to study the one-dimensional Dirac equation. An integral equation
which can be solved by iterative procedure to find the wave functions is
established. We employ this approach to study the one-dimensional Dirac
equation with one-well potential, and give the energy levels and wave functions
up to the first order iterative approximation. For double-well potential, the
energy levels up to the first order approximation are given.Comment: 3 figures, 21 page
Is the 130 GeV Line Real? A Search for Systematics in the Fermi-LAT Data
Our recent claims of a Galactic center feature in Fermi-LAT data at
approximately 130 GeV have prompted an avalanche of papers proposing
explanations ranging from dark matter annihilation to exotic pulsar winds.
Because of the importance of such interpretations for physics and astrophysics,
a discovery will require not only additional data, but a thorough investigation
of possible LAT systematics. While we do not have access to the details of each
event reconstruction, we do have information about each event from the public
event lists and spacecraft parameter files. These data allow us to search for
suspicious trends that could indicate a spurious signal. We consider several
hypotheses that might make an instrumental artifact more apparent at the
Galactic center, and find them implausible. We also search for an instrumental
signature in the Earth limb photons, which provide a smooth reference spectrum
for null tests. We find no significant 130 GeV feature in the Earth limb
sample. However, we do find a marginally significant 130 GeV feature in Earth
limb photons with a limited range of detector incidence angles. This raises
concerns about the 130 GeV Galactic center feature, even though we can think of
no plausible model of instrumental behavior that connects the two. A modest
amount of additional limb data would tell us if the limb feature is a
statistical fluke. If the limb feature persists, it would raise doubts about
the Pass 7 processing of E > 100 GeV events. At present we find no instrumental
systematics that could plausibly explain the excess Galactic center emission at
130 GeV.Comment: 16 pages, 22 figure
IceCube and HAWC constraints on very-high-energy emission from the Fermi bubbles
The nature of the -ray emission from the \emph{Fermi} bubbles is
unknown. Both hadronic and leptonic models have been formulated to explain the
peculiar -ray signal observed by the Fermi-LAT between 0.1-500~GeV. If
this emission continues above 30~TeV, hadronic models of the \emph{Fermi}
bubbles would provide a significant contribution to the high-energy neutrino
flux detected by the IceCube observatory. Even in models where leptonic
-rays produce the \emph{Fermi} bubbles flux at GeV energies, a hadronic
component may be observable at very high energies. The combination of IceCube
and HAWC measurements have the ability to distinguish these scenarios through a
comparison of the neutrino and -ray fluxes at a similar energy scale.
We examine the most recent four-year dataset produced by the IceCube
collaboration and find no evidence for neutrino emission originating from the
\emph{Fermi} bubbles. In particular, we find that previously suggested excesses
are consistent with the diffuse astrophysical background with a p-value of 0.22
(0.05 in an extreme scenario that all the IceCube events that overlap with the
bubbles come from them). Moreover, we show that existing and upcoming HAWC
observations provide independent constraints on any neutrino emission from the
\emph{Fermi} bubbles, due to the close correlation between the -ray and
neutrino fluxes in hadronic interactions. The combination of these results
disfavors a significant contribution from the \emph{Fermi} bubbles to the
IceCube neutrino flux.Comment: 9 pages, 4 figures, to appear in PR
Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50
degrees above and below the Galactic center, with a width of about 40 degrees
in longitude. The gamma-ray emission associated with these bubbles has a
significantly harder spectrum (dN/dE ~ E^-2) than the IC emission from
electrons in the Galactic disk, or the gamma-rays produced by decay of pions
from proton-ISM collisions. There is no significant spatial variation in the
spectrum or gamma-ray intensity within the bubbles, or between the north and
south bubbles. The bubbles are spatially correlated with the hard-spectrum
microwave excess known as the WMAP haze; the edges of the bubbles also line up
with features in the ROSAT X-ray maps at 1.5-2 keV. We argue that these
Galactic gamma-ray bubbles were most likely created by some large episode of
energy injection in the Galactic center, such as past accretion events onto the
central massive black hole, or a nuclear starburst in the last ~10 Myr. Dark
matter annihilation/decay seems unlikely to generate all the features of the
bubbles and the associated signals in WMAP and ROSAT; the bubbles must be
understood in order to use measurements of the diffuse gamma-ray emission in
the inner Galaxy as a probe of dark matter physics. Study of the origin and
evolution of the bubbles also has the potential to improve our understanding of
recent energetic events in the inner Galaxy and the high-latitude cosmic ray
population.Comment: 46 pages, 28 figures, accepted by Ap
Primordial B-mode Diagnostics and Self Calibrating the CMB Polarization
Distortions in the primordial cosmic microwave background (CMB) along the
line-of-sight can be modeled and described using 11 fields. These distortion
fields correspond to various cosmological signals such as weak gravitational
lensing of the CMB by large-scale structure, screening from patchy
reionization, rotation of the plane of polarization due to magnetic fields or
parity violating physics. Various instrumental systematics such as gain
fluctuations, pixel rotation, differential gain, pointing, differential
ellipticity are also described by the same distortion model. All these
distortions produce B-mode that contaminate the primordial tensor B-modes
signal. In this paper we show that apart from generating B-modes, each
distortion uniquely couples different modes (\bfl_1\ne \bfl_2) of the CMB
anisotropies, generating correlations which for the primordial CMB are
zero. We describe and implement unbiased minimum variance quadratic estimators
which using the off diagonal correlations in the CMB can extract the map of
distortions. We perform Monte-Carlo simulations to characterize the estimators
and illustrate the level of distortions that can be detected with current and
future experiments. The estimators can be used to look for cosmological
signals, or to check for any residual systematics in the data. As a specific
example of primordial tensor B-mode diagnostics we compare the level of minimum
detectable distortions using our method with maximum allowed distortion level
for the B-modes detection. We show that for any experiment, the distortions
will be detected at high significance using correlations before they would show
up as spurious B-modes in the power spectrum.Comment: 14 pages, 4 figure
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